Synergistic microbicidal combinations containing 4,5-dichloro-2-octyl-3-isothiazolone and certain commercial biocides

ABSTRACT

Synergistic microbicidal compositions are disclosed, comprising 4,5-dichloro-2-octyl-3-isothiazolone and one or more known microbicides for more effective, and broader control of microorganisms in various systems.

This is a division of application Ser. No. 591,316, filed Oct. 1, 1990,which is in turn a division of Ser. No. 431,367 of Nov. 2, 1989, bothnow abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention concerns microbicidal compositions which include anisothiazolone and one or more other biocides, and which are intended toprovide more effective and broader control of microorganisms in variousindustrial systems and for household products, agricultural products,and biomedical products, etc. In particular, the present inventionrelates to the use of a composition of2-n-octyl-4,5-dichloro-4-isothiazolin-3-one, hereinafter referred to as4,5-dichloro-2-octyl-3-isothiazolone, with one or more of the following11 compounds: 3-iodo-2-propynylbutylcarbamate,1,2-dibromo-2,4-dicyanobutane, p-tolyldiiodomethylsulfone,methylenebisthiocyanate, 2-thiocyanomethylthiobenzothiazole,tetrachloroisophthalonitrile, 2-n-octyl-3-isothiazolone,bis-(trichloromethyl)sulfone, 5-bromo-5-nitro-1,3-dioxane,2-bromo-2-nitropropanediol, 2,2-dibromo-3-nitrilopropionamide.

The term "microbicidal" (or "antimicrobial" or "biocidal") as usedherein is intended to encompass, but is not restricted to, allbactericidal, fungicidal and algicidal activity.

2. Prior Art

Isothiazolones are described in U.S. Pat. Nos. 3,761,488; 4,105,431;4,252,694; 4,265,899 and 4,279,762, and elsewhere. Their use asmicrobicides is well known.

It is the principal object of this invention to provide synergisticcompositions which overcome disadvantages of known microbicidalcompositions.

SUMMARY OF THE INVENTION

We have found that compositions formed from4,5-dichloro-2-octyl-3-isothiazolone and one or more of the 11 specifiedcompounds (supra) unexpectedly afford synergistic antimicrobial activityagainst a wide range of microorganisms: the disruptive action on theorganisms by the two compounds together is unexpectedly greater than thesum of both compounds taken alone. This synergy does not arise from theexpected activity of the components nor from the expected improvement inactivity. As a result of the synergy, the effective dose required can belowered, which is not only more economical but also increases safetymargins. The synergistic compositions of the present invention providemore effective and broader control of microorganisms in a number ofsystems.

The present invention thus provides a composition having microbicidalactivity which includes 4,5-dichloro-2-octyl-3-isothiazolone and asecond component selected from one or more of the group consisting of:3-iodo-2-propynylbutylcarbamate, 1,2-dibromo-2,4-dicyanobutane,p-tolyldiiodomethylsulfone, methylenebisthiocyanate,2-thiocyanomethylthiobenzothiazole, tetrachloroisophthalonitrile,2-n-octyl-3-isothiazolone, bis(trichloromethyl)sulfone,5-bromo-5-nitro-1,3-dioxane, 2-bromo-2-nitropropanediol,2,2-dibromo-3-nitrilopropionamide; wherein the weight ratio of4,5-dichloro-2-octyl-3-isothiazolone to the second component is fromabout 150:1 to 1:250.

Important applications of the synergistic antimicrobial compositions ofthe present invention include but are not limited to: inhibiting thegrowth of bacteria and fungi in aqueous paints and coatings, adhesives,sealants, latex emulsions, and joint cements; preserving wood;preserving cutting fluids, controlling slime-producing bacteria andfungi in pulp and papermills and cooling towers; as a spray or diptreatment for textiles and leather to prevent mold growth; protectingpaint films, especially exterior paints, from attack by fungi whichoccurs during weathering of the paint film; protecting processingequipment from slime deposits during manufacture of cane and beet sugar;preventing microorganism buildup and deposits in air washer or scrubbersystems and in industrial fresh water supply systems; preserving fuel;controlling microorganisms contamination and deposits in oil fielddrilling fluids and muds, and in secondary petroleum recovery processes;preventing bacterial and fungal growth in paper coatings and coatingprocesses; controlling bacterial and fungal growth and deposits duringthe manufacture of various specialty boards, e.g., cardboard andparticle board; preventing sap stain discoloration on freshly cut woodof various kinds; controlling bacterial and fungal growth in clay andpigment slurries of various types; as a hard surface disinfectant toprevent growth of bacteria and fungi on walls, floors, etc.; as apreservative for cosmetic and toiletry products, floor polishes, fabricsofteners, household and industrial products, in swimming pools toprevent algae growth; inhibiting the growth of harmful bacteria, yeasts,fungi on plants, trees, fruits, seeds, or soil; preserving agriculturalformulations, electrodeposition systems, diagnostic and reagentproducts, medical devices; protecting animal dip compositions againstthe buildup of microorganisms, and in photoprocessing to prevent buildupof microorganisms, and the like.

The compositions of the invention may be added separately to any systemor may be formulated as a simple mixture comprising its essentialingredients, and if desired a suitable carrier or solvent, or as anaqueous emulsion or dispersion.

The invention also provides a method of inhibiting the growth ofbacteria, fungi or algae in a locus subject to contamination bybacteria, fungi or algae, which comprises incorporating into or onto thelocus in an amount which is effective to adversely affect the growth ofbacteria, fungi or algae any of the compositions defined above.

GENERAL DESCRIPTION OF THE PREFERRED EMBODIMENT

The composition of the invention can be formulated as a solution in awide range of organic solvents. The solutions generally contain about 5to 30% by weight of the active composition. It is generally moreconvenient to provide the compositions in a water-diluted form: this maybe accomplished by adding an emulsifier to the organic solution followedby dilution with water.

In general, the weight ratio of 4,5-dichloro-2-octyl-3-isothiazolone tosecond component in the composition may be in the range of from about150:1 to about 1:250. The other specific and preferred ratios are givenin the examples.

The synergism of two-component compositions is demonstrated by testing awide range of concentrations and ratios of compounds, generated bytwo-fold serial dilutions in a Trypticase Soy Broth (Difco) growthmedium of a microbicide in one dimension and another microbicide in thesecond dimension, against a bacterium Escherichia coli (ATCC 11229), orfungi Candida albicans (ATCC 11651), Aspergillus niger (ATCC 6275), orAureobasidium pullulan (ATCC 9348). Each test tube was inoculated tomake about 1-5×10⁷ bacteria per ml or 1-5×10⁵ fungi per ml. The lowestconcentrations of each compound or mixtures to inhibit visible growth(turbidity) at 37° for E. coli and at 30° C. for the fungi for 7 dayswere taken as the minimum inhibitory concentration (MIC). The MIC weretaken as end points of activity. End points for the mixtures of compoundA (4,5-dichloro-2-octyl-3-isothiazolone) and compound B (secondcomponent microbicide) were then compared with the end points for theisothiazolone A alone and compound B alone. Synergism was determined bya commonly used and accepted method described by Kull, F. C.; Eisman, P.C.; Sylwestrowicz, H. D. and Mayer, R. L., in applied Microbiology9:538-541 (1961) using the ratio determined by

    Qa/QA+Qb/QB=Synergy Index (SI)

wherein

QA=concentration of compound A in parts per million (ppm), acting alone,which produced an end point.

Qa=concentration of compound A in ppm, in the mixture, which produced anend point.

QB=concentration of compound B in ppm, acting alone, which produced anend point.

Qb=concentration of compound B in ppm, in the mixture, which produced anend point

when the sum of Qa/QA and Qb/QB is greater than one, antagonism isindicated. When the sum is equal to one additivity is indicated, andwhen less than one synergism is demonstrated.

The test results for demonstration of synergism of microbicidecombinations are shown in Tables 1 to 11. Each table concerns thecombination of 4,5-dichloro-2-octyl-3-isothiazolone and one othermicrobicide, and shows:

1. the identity of the second microbicide (compound B);

2. test against E. coli, C. albicans (C. alb), A. niger or A. pullulan(A. pullul)

3. the end-point activity in ppm measured by MIC for compound A alone(QA), for compound B alone (QB), for compound A in the mixture (Qa), orfor compound B in the mixture (Qb);

4. the calculation of synergy index (SI) based on the formulaSI=Qa/QA+Qb/QB, and the weight ratio of 4,5-dichloro2-n-octyl-3-isothiazolone (compound A) to compound B in the particularcombination (A:B);

5. the range of weight ratios for synergism and the preferred weightratios. It will be appreciated by those skilled in the art that theratios given are approximate only.

The MIC values of each compound tested alone (QA or QB) are end-pointactivities except where the value is expressed as x.10. In these cases,the end-point activity was not seen at the highest tested concentration.For purpose of calculation of the synergy index and for operationaldefinition of MIC, the reported value is twice the highest testedconcentration. The value could be an underestimate of the true MIC;thus, the true synergy index could be even lower.

                  TABLE 1                                                         ______________________________________                                        Compound A = 4,5-dichloro-2-octyl-3-isothiazolone                             Compound B = 3-iodo-2-propynylbutylcarbamate                                  OR-                      calculations                                         GAN-   end-point activity in ppm                                                                       Qa/    Qb/                                           ISM    QA     QB      Qa   Qb    QA   QB   SI   A:B                           ______________________________________                                        A. niger                                                                             16.10  4.00    4.00 2.00  0.25 0.50 0.75 2:1                                  16.10  4.00    8.00 0.50  0.50 0.13 0.62 16:1                          A. pullul                                                                            16.10  2.00    8.00 0.25  0.50 0.13 0.62 32:1                          C. alb 16.00  4.00    8.00 2.00  0.50 0.50 1.00 4:1                           C. alb 2.00   8.00    0.25 4.00  0.13 0.50 0.63  1:16                         C. alb 4.10   16.10   2.00 4.00  0.49 0.25 0.74 1:2                           C. alb 32.10  16.00   4.00 8.00  0.12 0.50 0.62 1:2                                  32.10  16.00   16.00                                                                              2.00  0.50 0.13 0.62 8:1                           E. coli                                                                              16.00  250.00  8.00 125.00                                                                              0.50 0.50 1.00  1:16                         E. coli                                                                              8.00   250.00  4.00 62.00 0.50 0.25 0.75  1:16                         ______________________________________                                         Synergistic ratios of compound A:compound B range from 32:1 to 1:16;          preferred ratios are in the range 32:1 to 1:2.                           

                  TABLE 2                                                         ______________________________________                                        Compound A = 4,5-dichloro-2-octyl-3-isothiazolone                             Compound B = 1,2-dibromo-2,4-dicyanobutane                                    OR-                      calculations                                         GAN-   end-point activity in ppm                                                                       Qa/    Qb/                                           ISM    QA     QB      Qa   Qb    QA   QB   SI   A:B                           ______________________________________                                        C. alb 16.00  62.00   1.00 31.00 0.06 0.50 0.56  1:31                                16.00  62.00   8.00 16.00 0.50 0.26 0.76 1:2                           C. alb 4.00   32.00   1.00 8.00  0.25 0.25 0.50 1:8                                  4.00   32.00   2.00 1.00  0.50 0.03 0.53 2:1                           C. alb 4.10   31.00   2.00 8.00  0.49 0.26 0.75 1:4                           C. alb 32.10  125.00  16.00                                                                              16.00 0.50 0.13 0.63 1:1                           E. coli                                                                              16.00  62.00   8.00 16.00 0.50 0.26 0.76 1:2                           E. coli                                                                              8.00   62.00   4.00 31.00 0.50 0.50 1.00 1:8                           A. niger                                                                             16.10  64.10   8.00 16.00 0.50 0.25 0.75 1:2                           ______________________________________                                         Synergistic ratios of compound A:compound B range from 2:1 to 1:31,           preferred ratios are in the range of 2:1 to 1:2.                         

                  TABLE 3                                                         ______________________________________                                        Compound A = 4,5-dichloro-2-octyl-3-isothiazolone                             Compound B = p-tolyldiiodomethylsulfone                                       OR-                     calculations                                          GAN-  end-point activity in ppm                                                                       Qa/    Qb/                                            ISM   QA     QB      Qa   Qb    QA   QB   SI   A:B                            ______________________________________                                        C. alb                                                                              4.10   10.00   2.00 2.50  0.49 0.25 0.74 1:1.25                         C. alb                                                                              4.00   4.00    2.00 0.50  0.50 0.13 0.63 4:1                            E. coli                                                                             16.00  1000.10 8.00 125.00                                                                              0.50 0.12 0.62 1:16                           E. coli                                                                             8.00   1000.10 4.00 31.00 0.50 0.03 0.53 1:8                            A. nig-                                                                             16.10  16.00   8.00 8.00  0.50 0.50 1.00 1:1                            er                                                                            A. pull-                                                                            16.10  8.00    8.00 4.00  0.50 0.50 1.00 2:1                            ul                                                                            ______________________________________                                         Synergistic ratios of compound A:compound B range from 4:1 to 1:16;           preferred ratios are in the range 4:1 to 1:1.25                          

                  TABLE 4                                                         ______________________________________                                        Compound A = 4,5-dichloro-2-octyl-3-isothiazolone                             Compound B = methylenebisthiocyanate                                          OR-                     calculations                                          GAN-   end-point activity in ppm                                                                      Qa/    Qb/                                            ISM    QA     QB      Qa   Qb   QA   QB   SI   A:B                            ______________________________________                                        C. alb 16.00  125.10  8.00 62.00                                                                              0.50 0.50 1.00 1:8                            C. alb 4.00   32.00   2.00 2.00 0.50 0.06 0.56 1:1                            C. alb 32.10  62.00   16.00                                                                              8.00 0.50 0.13 0.63 2:1                            C. alb 4.10   31.00   2.00 16.00                                                                              0.49 0.52 1.00 1:8                            E. coli                                                                              16.00  125.00  0.50 62.00                                                                              0.03 0.50 0.53 1:125                          A. pullul                                                                            16.10  32.00   4.00 16.00                                                                              0.25 0.50 0.75 1:4                                   16.10  32.00   8.00 8.00 0.50 0.25 0.75 1:1                            ______________________________________                                         Synergistic ratios of compound A:compound B range from 2:1 to 1:125;          preferred ratios are in the range of 2:1 to 1:4.                         

                  TABLE 5                                                         ______________________________________                                        Compound A = 4,5-dichloro-2-octyl-3-isothiazolone                             Compound B = 2-thiocyanomethylthiobenzothiazole                               OR-                                                                           GAN-   end-point activity in ppm                                                                     calculations                                           ISM    QA     QB     Qa   Qb   Qa/QA Qb/QB SI   A:B                           ______________________________________                                        C. alb 32.10  8.00   16.00                                                                              4.00 0.50  0.50  1.00 4:1                           C. alb 2.00   8.00   0.25 4.00 0.13  0.50  0.63  1:16                         A. niger                                                                             16.10  32.10  2.00 16.00                                                                              0.12  0.50  0.62 1:8                                  16.10  32.10  8.00 2.00 0.50  0.06  0.56 4:1                           A. pullul                                                                            16.10  8.00   4.00 4.00 0.25  0.50  0.75 1:1                                  16.10  8.00   8.00 2.00 0.50  0.25  0.75 4:1                           ______________________________________                                         Synergistic ratios of compound A:compound B range from 4:1 to 1:16;           preferred ratios are in the range of 4:1 to 1:8.                         

                  TABLE 6                                                         ______________________________________                                        Compound A = 4,5-dichloro-2-octyl-3-isothiazolone                             Compound B = tetrachloroisophthalonitrile                                     OR-                                                                           GAN-   end-point activity in ppm                                                                     calculations                                           ISM    QA     QB     Qa   Qb   Qa/QA Qb/QB SI   A:B                           ______________________________________                                        C. alb 0.50   16.00  0.25 2.00 0.50  0.13  0.63 1:8                           A. niger                                                                             16.10  32.10  0.25 16.00                                                                              0.02  0.50  0.51  1:64                                16.10  32.10  8.00 0.50 0.50  0.02  0.51 16:1                          A. pullul                                                                            16.10  16.00  2.00 8.00 0.12  0.50  0.62 1:4                                  16.10  16.00  8.00 1.00 0.50  0.06  0.56 8:1                           C. alb 2.00   32.10  1.00 1.00 0.50  0.03  0.53 1:1                           ______________________________________                                         Synergistic ratios of compound A:compound B range from 16:1 to 1:64;          preferred ratios are in the range of 8:1 to 1:8.                         

                  TABLE 7                                                         ______________________________________                                        Compound A = 4,5-dichloro-2-octyl-3-isothiazolone                             Compound B = 2-n-octyl-3-isothiazolone                                        OR-                      calculations                                         GAN-   end-point activity in ppm                                                                       Qa/    Qb/                                           ISM    QA     QB      Qa   Qb    QA   QB   SI   A:B                           ______________________________________                                        C. alb 16.00  4.00    0.25 2.00  0.02 0.50 0.52 1:8                                  16.00  4.00    0.50 1.00  0.03 0.25 0.28 1:2                           C. alb 4.00   1.00    1.00 0.50  0.25 0.50 0.75 2:1                                  4.00   1.00    2.00 0.06  0.50 0.06 0.56 32:1                          C. alb 4.10   1.00    2.00 0.50  0.49 0.50 0.99 4:1                           C. alb 32.10  2.00    16.00                                                                              1.00  0.50 0.50 1.00 16:1                          E. coli                                                                              16.00  250.00  4.00 125.00                                                                              0.25 0.50 0.75  1:32                         E. coli                                                                              16.00  125.00  8.00 31.00 0.50 0.25 0.75 1:4                           A. pullul                                                                            16.10  8.00    4.00 4.00  0.25 0.50 0.75 1:1                                  16.10  8.00    8.00 1.00  0.50 0.13 0.62 8:1                           ______________________________________                                         Synergistic ratios of compound A:compound B range from 32:1 to 1:32;          preferred ratios are in the range of 8:1 to 1:2.                         

                  TABLE 8                                                         ______________________________________                                        Compound A = 4,5-dichloro-2-octyl-3-isothiazolone                             Compound B = bis-(trichloromethyl)sulfone                                     OR-                     calculations                                          GAN-  end-point activity in ppm                                                                       Qa/    Qb/                                            ISM   QA     QB      Qa   Qb    QA   QB   SI   A:B                            ______________________________________                                        C. alb                                                                              16.00  16.00   4.00 4.00  0.25 0.25 0.50 1:1                            C. alb                                                                              16.00  250.10  8.00 125.00                                                                              0.50 0.50 1.00 1:16                           E. coli                                                                             16.00  125.00  0.50 62.00 0.03 0.50 0.53 1:125                                16.00  125.00  4.00 31.00 0.25 0.25 0.50 1:8                                  16.00  125.00  8.00 16.00 0.50 0.13 0.63 1:2                            E. coli                                                                             16.00  1000.00 1.00 62.00 0.06 0.06 0.12 1:62                                 16.00  1000.00 2.00 31.00 0.13 0.03 0.16 1:16                                 16.00  1000.00 4.00 16.00 0.25 0.02 0.27 1:4                                  16.00  1000.00 8.00 1.00  0.50 0.00 0.50 8:1                            ______________________________________                                         Synergistic ratios of compound A:compound B range from 8:1 to 1:125;          preferred ratios are in the range of 8:1 to 1:8.                         

                  TABLE 9                                                         ______________________________________                                        Compound A = 4,5-dichloro-2-octyl-3-isothiazolone                             Compound B = 5-bromo-5-nitro-1,3-dioxane                                      OR-                     calculations                                          GAN-   end-point activity in ppm                                                                      Qa/    Qb/                                            ISM    QA     QB      Qa   Qb   QA   QB   SI   A:B                            ______________________________________                                        C. alb 4.10   50.00   1.00 25.00                                                                              0.24 0.50 0.74 1:25                                  4.10   50.00   2.00 6.20 0.49 0.12 0.61 1:3.1                          C. alb 16.00  100.00  0.25 50.00                                                                              0.02 0.50 0.52 1:200                                 16.00  100.00  0.50 25.00                                                                              0.03 0.25 0.28 1:50                                  16.00  100.00  2.00 12.50                                                                              0.13 0.13 0.25 1:6.2                          E. coli                                                                              8.00   100.00  1.00 50.00                                                                              0.13 0.50 0.63 1:50                                  8.00   100.00  4.00 25.00                                                                              0.50 0.25 0.75 1:6.2                          E. coli                                                                              16.00  50.00   2.00 25.00                                                                              0.13 0.50 0.63 1:12.5                                16.00  50.00   8.00 12.50                                                                              0.50 0.25 0.75 1:1.6                          ______________________________________                                         Synergistic ratios of compound A:compound B range from 2:1.6 to 1:200;        preferred ratios are in the range of 1:1.6 to 1:12.5.                    

                  TABLE 10                                                        ______________________________________                                        Compound A = 4,5-dichloro-2-octyl-3-isothiazolone                             Compound B = 2-bromo-2-nitropropanediol                                       OR-                     calculations                                          GAN-  end-point activity in ppm                                                                       Qa/    Qb/                                            ISM   QA     QB      Qa   Qb    QA   QB   SI   A:B                            ______________________________________                                        C. alb                                                                              4.10   100.10  0.50 50.00 0.12 0.50 0.62 1:100                                4.10   100.10  1.00 25.00 0.24 0.25 0.49 1:25                                 4.10   100.10  2.00 12.50 0.49 0.12 0.61 1:6.2                          C. alb                                                                              16.00  200.20  4.00 100.00                                                                              0.25 0.50 0.75 1:25                                 16.00  200.10  8.00 25.00 0.50 0.12 0.62 1:3.2                          E. coli                                                                             16.00  25.00   4.00 12.50 0.25 0.50 0.75 1:3.2                                16.00  25.00   8.00 3.10  0.50 0.12 0.62 1:0.4                          E. coli                                                                             16.00  25.00   4.00 12.50 0.25 0.50 0.75 1:3.2                                16.00  25.00   8.00 6.20  0.50 0.25 0.75 1:0.8                          ______________________________________                                         Synergistic ratios of compound A:compound B range from 1:0.4 to 1:100;        preferred ratios are in the range of 1:0.4 to 1:6.2.                     

                  TABLE 11                                                        ______________________________________                                        Compound A = 4,5-dichloro-2-octyl-3-isothiazolone                             Compound B = 2,2-dibromo-3-nitrilopropionamide                                OR-                     calculations                                          GAN-  end-point activity in ppm                                                                       Qa/    Qb/                                            ISM   QA     QB      Qa   Qb    QA   QB   SI   A:B                            ______________________________________                                        C. alb                                                                              4.10   250.00  0.50 125.00                                                                              0.12 0.50 0.62 1:250                                4.10   250.00  2.00 16.00 0.49 0.06 0.55 1:8                            C. alb                                                                              32.10  250.00  16.00                                                                              16.00 0.50 0.06 0.56 1:1                            E. coli                                                                             16.00  250.00  1.00 125.00                                                                              0.06 0.50 0.56 1:125                                16.00  250.00  8.00 16.00 0.50 0.06 0.56 1:2                            E. coli                                                                             8.00   250.00  1.00 125.00                                                                              0.13 0.50 0.63 1:125                                8.00   250.00  2.00 62.00 0.25 0.25 0.50 1:31                           ______________________________________                                         Synergistic ratios of compound A:compound B range from 1:1 to 1:250;          preferred ratios are in the range of 1:1 to 1:125.                       

As can be seen by review of Tables 1-11, the compositions of theinvention demonstrate synergistic microbicidal activity as measured byminimum inhibitory concentrations (MIC) and show surprisingly greateractivity than the algebraic sum of the individual components which makeup each composition.

In contrast, an example of non-synergistic combination of4,5-dichloro-2-octyl-3-isothiazolone and sodium dichlorophene is shownin Table 12. In this example of non-synergism, the microbial activitiesof either component as measured against E. coli and C. albicans are notaffected by the presence or the absence of the other component in thecombination. It is also not antagonistic because no loss of activity ofeither component in the combination was detected.

The synergistic activities of the compositions of the invention in mostcases are applicable to bacteria, fungi, and a mixture of bacteria andfungi. Thus, the combinations not only lower the use-level of biocidebut also broaden the spectrum of activity. This is especially useful insituations where either component alone does not achieve the bestresults due to weak activity against certain organisms.

                  TABLE 12                                                        ______________________________________                                        (comparative)                                                                 Compound A = 4,5-dichloro-2-octyl-3-isothiazolone                             Compound B = Sodium dichlorophene                                             OR-                                                                           GAN-   end-point activity in ppm                                                                      calculations                                          ISM    QA     QB     Qa     Qb  Qa/QA Qb/QB SI  A:B                           ______________________________________                                        C. alb 4.10   16.00  No effect                                                C. alb 16.00  32.00  No effect                                                E. coli                                                                              16.00  62.00  No effect                                                ______________________________________                                    

What is claimed is:
 1. A microbicidal composition the first component ofwhich is 4,5-dichloro-2-octyl-3-isothiazolone and the second componentis 2-bromo-2-nitropropanediol; wherein the weight ratio of the firstcomponent to second component is in the range of from about 1:0.4 toabout 1:100.
 2. The composition of claim 1, wherein the ratio of thefirst component to the second component, 2-bromo-2-nitropropanediol, isin the range of from about 1:0.4 to about 1:6.2.